In order to increase transistor device speed, conventional SiO2 gate oxides have been scaled aggressively. As SiO2 thickness decreases, the gate leakage current increases significantly due to the direct tunneling as the primary conduction mechanism. One way to decrease the leakage current is to use a gate dielectric with a high dielectric constant, k, so that we can make a physically thick film with the same electrical thickness as SiO2 films. The quality of metal oxide is not as structurally desirable as SiO2 because the high dielectric constant film is fabricated by a deposition method rather than being thermally grown. It is known that the electrical properties of deposition films are inherently inferior to deposition grown films. Therefore, a need exists to improve the quality of high dielectric constant materials.
Typically the film quality is improved by a high temperature post deposition anneal (PDA) step in either an O2 or an N2 ambient. This approach has at least two disadvantages. Firstly, it will increase the interfacial thickness if an O2 PDA is used. Secondly, the efficiency of passivating existing dangling bonds is not effective with this process. In addition, most deposition precursors contain undesirable impurities such as carbon and hydrogen. The carbon and hydrogen will degrade the metal oxide film quality.
CMOS devices suffer from boron penetration for PMOS transistors. It is more problematic for polycrystalline metal oxide structures. One way to minimize boron penetration is to incorporate nitrogen to the film because nitrogen is a known dopant diffusion barrier. Another advantage of nitrogen incorporation is to increase the polycrystalline temperature of high k materials.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.